gas exchange Flashcards
what are the two major adaptations of gas exchange surfaces
they have a large surface area
they’re thin (often just one layer of epithelial cells) - provides a short diffusion pathway across the gas exchange surface
what do single-celled organisms do
they absorb and release gases by diffusion through their outer surface
they have a relatively large surface area, a thin surface and a short diffusion pathway - no need for a gas exchange system
what type of system do fish use
counter-current system
stages of fish gas exchange
water, containing oxygen, enters the fish through its mouth and passes out through the gills
each gill is made of lots of thin plates, called gill filaments, which give a big surface area for exchange of gases
the gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more
lamellae adaptations
the lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion
why is it a counter-current system for fish
blood flows through the lamellae in one direction and water flows over in the opposite direction - counter-current
this maintains a large concentration gradient between the water and the blood
the concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood
what do insects use for gas exchange
microscopic air-filled pipes called tracheae
stages of gas exchange in insects
air moves into the tracheae through pores on the surface called spiracles
oxygen travels down the concentration gradient towards the cells
the tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells - this means that oxygen diffusion directly into the respiring cells
carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released into the atmosphere
insects use rhythmic abdominal movements to move air in and out of the spiracles
gas exchange for plants
the main gas exchange surface is the surface of the mesophyll cells in the leaf
- adapted as they have a large surface area
mesophyll cells are inside the leaf - gases move in and out through special pores in the epidermis called stomata
the stomata can open to allow exchange of gases, and close if the plant is losing too much water
guard cells control the opening and closing of stomata
how do insects control water loss
they close their spiracles using muscles - also have a waterproof waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation
how do plants control water loss
plants’ stomata are usually kept open during the day to allow gaseous exchange. water enters the guard cells, making them turgid, which opens the stomatal pore - if the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore
what pants are specially adapted for dry habitats
xerophytes
stomata sunk in pits that trap moist air - reducing the concentration gradient between leaf and air
a layer of ‘hairs’ on the epidermis - trap moist air
curled leaves with the stomata inside - protecting them from wind (wind increases rate of diffusion and evaporation)
a reduced number of stomata - fewer places for water to escape
waxy, waterproof cuticles to reduce evaporation
what are lungs specialised
as you breath in, air enters the trachea
the trachea splits into two bronchi - one bronchus leading to each lung
each bronchus then branches off into smaller tubes called bronchioles
the bronchioles end in small ‘air sacs’ called alveoli
the ribcage, intercostal muscles and diaphragm all work together to move air in and out
inhalation
the external intercostal and diaphragm muscles contract
this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity
as the volume of the thoracic cavity increases, the lung pressure decreases
air will flow - high pressure to low pressure - air flows from trachea into the lungs
active process - requires energy
exhalation
external intercostal and diaphragm muscles relax
ribcage - moves downwards and inwards
diaphragm becomes curved again
volume of thoracic cavity - decreases - air pressure increases
air is forced down the pressure gradient and out of lungs
passive process
